Triangle Partition

Chiaki has $3n$ points $p_1,p_2,\dots,p_{3n}$. It is guaranteed that no three points are collinear.
Chiaki would like to construct $n$ disjoint triangles where each vertex comes from the $3n$ points.

There are multiple test cases. The first line of input contains an integer $T$, indicating the number of test cases. For each test case:
The first line contains an integer $n$ ($1 \le n \le 1000$) -- the number of triangle to construct.
Each of the next $3n$ lines contains two integers $x_i$ and $y_i$ ($-10^9 \le x_i, y_i \le 10^9$).
It is guaranteed that the sum of all $n$ does not exceed $10000$.

For each test case, output $n$ lines contain three integers $a_i,b_i,c_i$ ($1 \le a_i,b_i,c_i \le 3n$) each denoting the indices of points the $i$-th triangle use. If there are multiple solutions, you can output any of them.

1
1
1 2
2 3
3 5

1 2 3

2018 Multi-University Training Contest 1